The present invention relates to methods and material for facilitating the handling of a plurality of high hardness fibers of the boron filament type of aggregating a plurality of them as groups or fascicles of filaments in an alloy metal matrix to form nuggets, continuous tapes or similar bundles of filaments fixed therein as a solid unit or preform. A plurality of such units then may be easily handled and aggregated and bonded together into larger shapes or forms to produce completed composite structures, e.g., cutting tools.
The boron filaments referred to herein are thin fibers or filaments of substantially elemental boron usually produced by vapor deposition of the boron on a core of fine tungsten wire. The wire acts as a substrate for depositing or growth of the boron as a filament or fiber having a crystallographic internal structure. The filaments are characterized by the ability to wear to fracture along their crystal or lattice fracture planes such that each filament always presents a sharp edge at the tip end being thus useful for cutting or abrading of materials if properly supported. The filaments are also characterized by high tensile strength but have low ductility and tend to break under shearing impact where adequate side support is lacking. As used herein "cutting" is intended as inclusive of cutting, abrading, grinding, polishing, shearing, honing, or the like operations.
Heretofore a number of methods and materials have been proposed for fabricating boron-filament containing matrices for structural or cutting tool use. Such prior methods have often required the filaments to be aggregated together in the matrix material by slow, tedious placement and arrangement of the individual short lengths of filaments in the form and volume finally desired in the final structure. They are then bonded by application of powder metallurgy, casting or hot pressing techniques into the finished product. Several disadvantages proceed from the prior methods which require generally individual handling of all the filaments in order to make final assembly of usable structure. These include slow production, high unit cost leading to requirement for complicated equipment, and the difficulty in obtaining a high volume percentage of the filaments in the matrices used to bond them together. Also maximum handling of a large number of the individual sharp filaments is a safety hazard in that they may stick to or penetrate the skin of personnel so handling them. A good-wearing metal matrix material that can be alloyed about the filaments without degrading their cutting qualities has also been sought for supporting the filaments in a solid mass to produce good tools and structures.